Getting a second opinion, am I being too ambitious?

Heading up to Maine to do some backpacking with some friends in August. Not new to backpacking but pretty new to planning the trips. As I plan this trip I am trying to jam as much into the last day as possible. I am going with a group of relatively athletic 20 year olds. All have hiked before and most are very athletic, However I am the only one who has been backpacking. For the final day of our trip I think we are going to wake up early (5am) and summit two mountains, roughly 4,850 ft in elevation gain over 8.5 miles and much of the ascent will be scrambling. We will also have our packs (should be relatively light as it is our last day and we won't be using a tent). With relatively young and in-shape crew, does this sound like an obtainable goal in say 9 hours (with occasional breaks)?

Thanks